Thank you so much for taking this kitty in. If I can just suggest one thing that may be in the cats best interest? Can you take it to a vet and have them scan for a chip? Sphyinx kitties are not too common so I would imagine he may have gotten out of someone's house and they amy be looking for him? If you take it to the humance society they are likely full to capacity and have limited numbers. He may only have a couple of days there and be euthanized. If he is chipped he has a better chance at being reunited with his owners.

"UNTIL ONE HAS LOVED AN ANIMAL, PART OF THEIR SOUL REMAINS UNAWAKENED"
He is your friend, your partner, your defender, your dog. You are his life, his love, his leader. He will be yours, faithful and true, to the last beat of his heart. You owe it to him to be worthy of such devotion.
-Unknown